1. Field of the Invention
This invention relates to electrohydraulic actuator systems and, more particularly, to such systems for positioning the nozzle of an associated turbine.
2. Description of the Prior Art
The development of a satisfactory gas turbine engine for automotive vehicle power depends to a significant extent upon the effectiveness of its control system. To compete successfully as an alternative to the already highly-developed piston engine as a vehicle power source, the gas turbine must not only be capable of comparable performance under all operating conditions, but preferably in a way and with a type of response which is familiar to the conditioned user of a piston engine-powered vehicle.
Most of the techniques required to satisfactorily control an automatic gas turbine are available from past experience with aircraft gas turbine engines. In a sense, the control system design may be more difficult because of the use by less sophisticated operators and the fact that is is practically necessary to cause the control system to simulate piston engine operation in the operator-machine interface. However, a more difficult problem is to realize the required control functions in devices which are acceptable on an economic basis for automotive utilization. Accordingly, many of the control devices and designs which are devised for use with gas turbine aircraft engines cannot be directly adapted to automotive use.
One of the particular control functions required for the automotive gas turbine engine is the positioning of the power turbine nozzles. Engine fuel flow and turbine nozzle position are controlled in response to various control and condition parameters such as accelerator pedal position, ambient temperature, ambient pressure, gas generator speed, gas generator turbine temperature, regenerator "hot side in" temperature, and transmission output shaft velocity. Because of the complexity of the control requirements, a computer is employed to operate with signals from a multiplicity of sensors and to develop the requisite control functions. Suitable actuators are required to operate in response to the computer control signals. Various types of electromechanical actuators are known, directed to a variety of output functions. Among these are the devices disclosed in the following U.S. Pat. Nos.: 2,055,209 of Schaer; 2,256,970 of Bryant; 2,570,624 of Wyckoff; 2,696,196 of Adams et al; 2,738,772 of Richter; 2,886,010 of Hayos et al; 3,264,947 of Bidlack; and 3,380,394 of Fornerod. Such prior art is exemplary of the technology to which the present invention relates.